Oxalic acid rust removal failures

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us56456712

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A few years ago I tried oxalic acid on my bike parts and I got a green stain where there was rust that nothing will take off. Someone on RRB said my mix was too concentrated. I threw out the ugly green parts. I dug out the acid last spring and used for deck wood bleach. Worked great. The net said to remove rust use one tablespoon per pint of water. That was more concentrated than what ruined my parts. I tried 3/4 teaspoon in two pints and removed the part every hour and washed off the green film. After 6 hours it’s green and won’t come off. All I can figure is that 1, the oxalic acid is reacting with the nickel plating making a green stain or 2, I need to use the one tablespoon per pint of water ratio and leave it in for only a half hour or so. The part that is now green still has some rust in the bottom of the green pits. Not a good rust removal result.
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Any ideas?
 

ingola

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A few years ago I tried oxalic acid on my bike parts and I got a green stain where there was rust that nothing will take off. Someone on RRB said my mix was too concentrated. I threw out the ugly green parts. I dug out the acid last spring and used for deck wood bleach. Worked great. The net said to remove rust use one tablespoon per pint of water. That was more concentrated than what ruined my parts. I tried 3/4 teaspoon in two pints and removed the part every hour and washed off the green film. After 6 hours it’s green and won’t come off. All I can figure is that 1, the oxalic acid is reacting with the nickel plating making a green stain or 2, I need to use the one tablespoon per pint of water ratio and leave it in for only a half hour or so. The part that is now green still has some rust in the bottom of the green pits. Not a good rust removal result. View attachment 216720 Any ideas?
Put it back in and agitate it the green should come off also it's wise to neutralize with backing soda when done use citric acid on parts it's less aggressive and actually takes less time and reusable
 

ingola

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What I've actually done with citric acid is got a waterproof massager (amazon) you can get them for 9 bucks throw at the bottom of the container it will agitated the the dirt and rust off. The green I believe is dirt turn by the acid.
 

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Put it back in and agitate it the green should come off also it's wise to neutralize with backing soda when done use citric acid on parts it's less aggressive and actually takes less time and reusable
If I remember correctly citric acid turned my parts yellow instead of green. Vinegar is way more corrosive, getting under the nickel and peeling it off but the staining is black, which is acceptable, green and yellow aren’t. Vinegar won’t remove the green or yellow staining or will brass brush scrubbing, it’s too deep in small pits. One of my friends uses muriatic acid for a short time. I have only used that on very rusty gas pipe cruiser frames.
 

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I use oxalic acid on glass but I use phosphoric acid on steel.

If you’ve got something chrome, it’s gonna blacken the pits and edges. Then you have to rub it with aluminum foil.

But I haven’t done a lot of work with rusty plated metal. That’s the only thing I know to do.

I found that different penetrating oils can have different acids, which cause different reactions. Carburetor dip always had Crysalic acid in it, I don’t know what it has nowadays. That was good for brightening up some alloy parts. Sometimes you got a green or yellow staining. I think it had something to do with how much zinc was in the metal.
 

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Maybe throw it in Evaporust? I use Evaporust on my smaller parts because it's too expensive for big stuff. But when I do big stuff, I watch the concentration of the Oxalic acid and immediately wash it off when done. I had a pair of cranks that were green. I buffed it off. It took a lot of work, but the cranks looks great.
 

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